Aircraft navigation and instrument landing system



y 1952 o. s. FIELD ETAL 2,597,784

AIRCRAFT NAVIGATION AND INSTRUMENT LANDING SYSTEM Filed Oct. 11, 1944 5 Sheets-Sheet l 1 Summers 1779/7 (Ittorneg May 20, 1952 O. S. FIELD ET AL AIRCRAFT NAVIGATION AND INSTRUMENT LANDING SYSTEM Filed Oct. 11, 1944 5 Sheets-Sheet 2 FIG. 4

31mm tors T/Ie/r Gttorneg y 1952 o. s. FIELD ETAL 2,597,784

AIRCRAFT NAVIGATION AND INSTRUMENT LANDING SYSTEM Filed 001;. 11, 1944 5 Sheegs-Sheeu 3 The/r Gttorneg May 20, 1952 o. s. FIELD ET AL 2,597,784

AIRCRAFT NAVIGATION AND INSTRUMENT LANDING SYSTEM Filed Oct. 11, 1944 5 Sheets-Sheet 4 FIG. 15

Snuentors wzzm fie/2' Qttomeg May 20, 1952 o. s. FIELD ETAL AIRCRAFT NAVIGATION AND INSTRUMENT LANDING SYSTEM Filed Oct. 11. 1944 3nnentots 5 Sheets-Sheet 5 llllll'llll @Ifi/d awdff/W/q/if 7/72/2- (Ittorneg \\3 F k M QM 3% msks i Patented May 20, 1952 UNITED STATES TENT OFFICE AIRCRAFT NAVIGATION AND INSTRUMENT LANDING SYSTEM Application October 11, 1944, Serial No. 558,256

14 Claims. 1

This invention relates to blind route'flying and blind landing instrumentalities and more particularly to a system for this purpose wherein the field of view ahead of the airplane is pictorially reproduced by mechanically scanning and plotting this field of view in one plane and by plotting in another plane distances proportional to the distance to the radio radiator on the ground and reproduced on the screen of a cathode ray oscillograph.

Insofar as route flying is concerned this application is an improvement over the prior application of Field, Wight and Saint, Ser. No. 517,814, filed January 11, 1944, which has resulted in Patent No. 2,463,094, dated March 3, 1949, and the prior application of Dicke, Ser. No. 532,181, filed April 21, 1944, which has resulted in Patent No. 2,439,846, dated April 20, 1948, whereas the portion of the disclosure relating to blind landing is an improvement over the prior application of Field and Wight, Ser. No. 548,660, filed August 9, 1944, which has resulted in Patent No. 2,463,095,

dated March 3, 1949, and no claim is made herein to that which is disclosed in any of these applica tions.

In the prior applications of Field, Wight and Saint, and of Dicke, apparatus for mechanically scanning at both a low speed and a high speed and in two different planes were provided. According to one embodiment of the present invention, however, mechanical scanning by a scanning antenna is in but one plane at a relatively low rate, and scanning for the other plane of the screen of a cathode-ray tube is provided electronically at a relatively high rate whereby distances measured by the excursion times of radio pulses are plotted.

In accordance with the present invention it is proposed to mechanically scan horizontally and plot vertically in accordance with the distance the scanned radiator is from the airplane, such scanning being preferably used for route flying. For blind landing it is proposed to mechanically scan vertically and then plot along horizontal lines on the screen of the cathode-ray oscillograph an image at a distance from one edge of the screen dependent on the distance from the airplane to the ground located radiator that is being scanned.

Another object of the present invention resides in the provision of means for coding the radiated energy that is radiated from radio radiators located on opposite sides of a landing strip of an airport, by coding of the radiators on one side of the landing strip to the code character A and by coding the radiators on the opposite side of the landing strip to the code character N as a result of which if two such ground located radio radiators are reproduced on the screen at the same point the codes of the two images will blend into each other to render the image non-coded.

Another object of the present invention resides in the provision of lines and marks on the cathode-ray tube screen whereby the pilot will be informed during a landing operation as to whether he is lined up straight with the landing strip upon which he is to land and whether or not he is following a prescribed glide path and also when he reaches the end of such glide path where his wheels will just touch the ground.

Another object of the present invention resides in the provision of means including mechanical scanning means on an airplane which will radiate forwardly of the airplane successive energy pulses successively in different directions and to provide receiving apparatus for detecting the time of return of pulses either originating ,on the ground or reflected from a ground located radio reflector, as a result of which the time of radiation from the airplane to the ground located radiator and from the ground located radiator to the airplane may be measured to determine the distance from the airplane to such ground located radiator. More specifically, it is proposed to provide a double antenna scanning apparatus of which one antenna is used to emit ultra-high-frequency radio pulse intermittently and to employ the other antenna for receiving radio energy emitted by a ground located radio radiator rendered active in response to the reception of such pulses. It may be desirable to accomplish these two functions by the same antenna. In one form of the invention it is proposed to emit modulated ultrahigh-frequency radio energy intermittently by the airplane carried apparatus and to normally radiate unmodulated ultra-high-frequency radio energy by each of the various ground located radiators and to provide other means at the ground located radio radiator for modulating the emitted ultra-high-frequency radio energy only when correspondingly modulated radio energy reaches such ground located apparatus, the airplane carried apparatus being so constructed that it will only manifest the reception of ultra-high-frequency energy when such energy has been modulated at the same frequency as was the radio energy emitted by that airplane carried apparatus.

Another object of the present invention resides in the provision of means to determine the frequency of modulation of the radio energy emitted by the airplane in accordance with the altitude at which the airplane is flying which is preferably accomplished by inserting tuned units in the transmitting and receiving circuits through the medium of altimeter controlled contacts.

Another object and purpose of the present invention resides in the provision of means for so mounting the mechanical scanning apparatus on the airplane that it may at one time mechanically scan in one plane and at another time may mechanically scan in a plane substantially at right-angles to such one plane, and to provide means for making the necessary circuit changes to cause the direction of fast scanning and slow scanning of the electron beam in the cathode-ray tube to be changed correspondingly.

Another object of the present invention resides in the provision of suitable coding 'means for each of the ground located radio radiators along the route so that the emitted "energy may be coded to identify that radiator substantially in accordance with the teachings of the prior application of Field, Wight and Saint, above referred to, to which attention is directed and which constitutes a portion of the system of the present invention.

Another object of the present invention resides in the provision of suitable means for using a portion of the same cathode-ray tube screen that is used for blind flying and blind landing to display thereon an artificial horizon, together With means for so displaying the artificial horizon in the upper or any other portion of the cathode-ray tube screen irrespective of whether the apparatus is adjusted to its horizontal mechanical scanning or its ertical mechanical scanning condition.

Other objects, purposes and characteristic features of the present invention will in part be described hereinafter and will in part be obvious from this description in combination with the accompanying drawings, in which:

Fig. 1 illustrates one embodiment of airplane carried apparatus embodying the present inven-' tion with the artificial horizon display apparatus omitted;

Fig. 2 shows a side elevation of a. ground located radio reflector together with means for mechanically operating such reflector to effective and non-efiective positions in accordance with a prescribed code;

Fig. 3 is a cross-sectional View of the reflector shown in Fig. 2 along the dotted line 3-3 when viewed in the direction of the arrows;

Fig. 4 shows conventionally one form of ground located radio receiving and radio transmitting apparatus constituting the necessary apparatus for one route defining radio radiator;

Fig. 5 shows graphs to illustrate sine-wave sweep-voltage frequency, pulsing current of the same frequency, a rectified pulse frequency wave, a saw-tooth wave, an intermittent radiated carrier frequency wave, and a continuous but intermittently modulated received carrier frequency radio wave, together with graph magnifying glasses to show a portion of these graphs enlarged; P

Fig. 5A shows the voltage graph for low speed Figs. 8 to 13 illustrate the same fluorescent screen as shown in Fig. 6 with six difierent landing indications depicted. thereon;

Fig. 14 illustrates a modification of the Fig. 4 structure which provided additional means for rendering the ground radiating radio active only when energy emitted from an airplane is received;

Fig. 15 illustrates conventionally all of the apparatus of Fig. 1 (parts omitted) and illustrates additional apparatus superimposed thereon for Visually indicating an artificial horizon on the upper part of the screen, as determined by an airplane carried gyroscope;

Fig. 16 shows the artificial horizon image in .the upper portion of the screen when the airspeed vertical scanning conditions;

Fig. 17 shows the artificial horizon image under similar conditions as in Fig. 16 except that the airplane is nosing downwardly;

Fig. 18 shows the artificial horizon image under similar conditions as in Fig.16 except that theairplane is banking toward the left;

Fig. 7 19' shows the artificial horizon image under similar conditions as in Fig. 18 except that the airplane is banking toward the right;

Figs. 20--23 show artificial horizon indications the same as those shown in Figs. 16-19 except that high speed scanning is in a horizontal plane instead of a vertical: plane.

Airplane carried structure In accordance with one form of the present invention all airplanes are preferably equipped with suitable radio transmitting apparatus and suitable radio receiving apparatus. Although, as shown the radio transmitting and radio receiving antennas TA and RA are of the scanning ty e it should be'understood that one of these antennas may be stationary, if desired. Also, one may be omitted and the retained one may be "used alternately for transmitting 'andreceiving.

' RAI and RA2 which are similarly supported by scanning on a different scale than is used in Fig. 5;

Fig. 6 illustrates a landing strip provided with two radio radiators coded at an A code and two radio radiators coded at an N code together landing purposes disposed at two different angles a with respect to the landing strip;

this shaft. This shaft II also supports an armature Ar of a sweep-voltage generator SG in= eluding a permanent magnet field structure hav ing poles s and n and a commutator including segments 12 and I3 which are engaged by stationary brushes I4 and I5. These brushes I4 and 15 are not so oriented with the field structure 'n-s as to produce direct current as is usually the case but are so oriented as to commutate the current when the voltage is a maximum, this in order to "create an alternating sweep voltage of the wave form substantially as shown in Fig. 5A of the drawings.

The transmitting antennas TAI and TA2,

which are preferably of parabolic gutter shape, are provided with a similar commutator including commutator segments I7 and I8 which cooperate with a single fixed brush I9 so as to apply-the radio transmitting-energy derived from -mixer and amplifier 213 only to the forwardly disposed antenna TAI or TA2 as the shaft II is rotated. In a similar manner the receiving antennas 'RAl and HA2 are provided with a commutator including commutator segments 2! and 22 which cooperate with a single stationary brush 23 which conducts the received radio energy to the receiver amplifier 25 tuned to a suitable carrier frequency such as frequency F2. As illustrated the radio transmitting antennas TAI and TA2 are separated from the radio receiving antennas RAl and RAZ by a suitable shield 21 which has been shown mounted on the shaft II, but which in practice may be supported by a stationary support.

The shaft H is supported in the bearings of the driving motor M which driving motor M also supports the permanent magnet field structure n-s of the sweep generator SG as by brackets'28 and 29. This'driving motor M is supported pivotally in bearings 33 and 34 so as to be rotatable about an axis parallel to the flight axis of the airplane AP. As illustrated brackets 3| and 32 support the bearing blocks 33 and 34 and these bearing blocks 33 and 34 rotatably support stub shafts 35 and 35 which are bolted or otherwise secured to the motor M so as to constitute the pivotal supporting means for the motor M as above mentioned.

The stub shaft 35 is provided with a handle 38 which is shown in its normal route flying position in solid lines and which has been shown in its 90 displaced blind landing position by the dotted lines 38. On the stub shaft 35 is secured an insulating drum 39 provided with suitable contact segments of conducting material directly connected to leads extending from the sweep voltage generator SG and from the sawtooth generator 40. The sweep plates 4|, 42, 43 and 44 of the cathode-ray tube K are connected to brushes shown by arrows so that connections may be made in two different relationships depending upon whether the handle 38 assumes its solid line or its dotted position. In other words, when the handle 38 assumes its solid line position the lead wires from the scanning generator SG connect to the horizontal sweep plates 42 and 44 whereas the saw-tooth generator 43 is then connected to the vertical sweep plates 4!. and 43. If, however, the handle 38 is moved to its dotted position the sweep generator SG will be connected to the vertical sweep plates 4i and 43 whereas the saw-tooth generator 43 will be connected to the horizontal sweep plates 42 and 44 of the cathode-ray tube or kinescope K. This kinescope K includes the usual fluorescent screen S and anode 43 and an electron-gun including an electron-focusing element 4?, a grid 48, and a cathode 49. This cathode 49 is preferably of the heater type including a closed metallic hood which is heated by a filament contained within the hood. As shown, the cathode 49 is heated by energy deriving from the battery 30.

It will be seen that the positive terminal of a plate source (-1-) is connected to the anode 46. This is done in order to aid in the acceleration of the electrons as they leave the cathode 49 to eventually impinge upon the fluorescent screen S. The sweep plates 4l-44 are of course used to sweep the electron beam illustrated by a dotand-dash line 53 in a manner so as to scan this entire screen as is well known in the electronic and television art and in accordance with sweep voltages generated by sweep voltage or scanning generators SG and 43.

As illustrated, focusing of the electron beam is accomplished by adjusting the potentiometer including the resistance Rl which is energized by the direct current source Bp. It is thus seen that the sweep plates are energized from the saw-toothed generator 40 and from the scanning generator SG and that the grid 48 may be controlled by energy derived from the radio receiver presently to be described through the medium of the wire 58.

This receiver 25 comprises receiving apparatus of conventional form designed to receive ultrahigh frequency radio energy of carrier frequency F2 which energy is then supplied, as through wire 5|, to the amplifier and detector portion 33 of the receiving apparatus, where this radio energy is amplified and rectified after which its modulated resultant energy if of proper modulating frequency flows through one of the filters 52, 53 or 54 providing the received energy is modulated to one of these frequencies fl, f2 or f3. If this modulating frequency is of frequency fl, for instance, it will flow through altimeter operated contact 51' and wire 58 to the grid 4-3 of the cathode-ray tube K. This flow of energy will fire the tube K, so to speak, to thereby render the electron beam 50 very pronounced, as a result of which a lighted spot will appear at that point on the screen S where the electron beam 53 is pointing at that time.

Let us now consider the question of how radio energy is generated on the airplane for transmission to a ground located radio receiver through the medium of antennas TAI or TAZ. As conventionally shown by the modulated energy emitted by transmitting antenna TAI (Fig. 1 and graph 16, Fig. 5) this radio energy is of ultra-high carrier frequency and of a modulating frequency preferably considerably above the audio range.

Referring to Fig. 1, the block diagram 55 illustrates a well-known ultra-high frequency radio oscillator for generating such ultra-high frequency current preferably of a frequency Fl. This carrier frequency may be generated by tube oscillators well known in the art as, for instance, are described at pages 480 to 530 of Radio Engineers Handbook by Terman, 1943 edition by McGraw-I-Iill Book Co.; or at page 484 of Television by Zworykin and Morton, 1940 edition by John Wiley and sons, New York. see also pages 192-215 of Fundamentals of Radio also by Terman.

Since, however, this radio carrier frequency is desired to be only intermittently applied this carrier frequency generator (for generating frequencies Fl) is preferably intermittently fired as through the medium of a gas filled tube, such as a thyratron, receiving energy from the pulse generator 35. This pulse generator 65 is of wellknown construction and may be of any suitable construction such for instance as disclosed on pages 514 and 515 of the Radio Engineers Handbook, by Terman, 1943 edition, or as disclosed on pages 214 and 215 of Fundamentals of Radio, 1938 edition, also by Mr. Terman. This pulse generator, if of electronic construction, is preferably controlled by a scanning frequency generator generating scanning radio energy of frequency F3 and conventionally shown by block 60 in Fig. 1 of the drawings. Since it is desired to make a vertical electron beam sweep at the instant a radio impulse is transmitted toward a ground located radio receiver it is of course understood that the electron beam 59 of the cathode-ray tube K must also be synchronized with the pulse generator 65. For this rea- 7 son the saw-tooth generator 4'0 is fired by cur rent derived from the pulse generator 65. This saw-tooth generator then generates current of saw-tooth configuration as illustrated at pages 416-419 and 514-515 of Fundamentals of Radio and Engineers Handbook, respectively and as shown by graph 14 in Fig. of the drawings.

It will be seen that the carrier frequency generator 55 which generates ultra-high radio carrier frequency, causes this high frequency energy to flow into a mixer and amplifier unit 29 at which point this radio carrier frequency is modulated to modulating frequencies fl, ft or 13 radio energy but preferably of frequency F2. The airplane carried apparatus isfhowever, not limited to such a construction and, if desired, theradiated and the received radio energies may be of the same carrier frequency. If the latter construction is employed the ground location may be provided with a radio reflector 85 (see Figs. 2 and 3) which consists'of three smooth surfaced 7 planes of radio reflecting material two of which depending upon the position then assumed by the altimeter controlled contact 59. For further information as to this altimeter controlled contact attention is directed to our prior application, Ser. No. 547,175, filed July 29, 1944. These modulating frequencies fl f2 and f3 are produced through the medium of filters El, 62 and 53 respectively. For methods of modulation by either heterodyne (p. 233) or the amplitude method (p. 219) attention is directed to these pages of Fundamentals of Radio referred to above.

Referring now to Figs. 5 and 5A of the drawings, attention is directed to the fact that the voltage curve or graph 70 generated by the scanning generator SG is of a form substantially as illustrated in Fig. 5A of the drawings whereas the graph ll illustrates the wave form of a sine wave scanning frequency voltage generated by scanning frequency generator 99. The graph i2 illustrates the alternating pulse voltage first generated by the pulse generator 65, which graph is then followed by a graph H of the uni-polarity pulse pulsating current which is obtained by rectifying the voltage of graph l2. The sawtooth graph 74 illustrates the wave form of the voltage generated by generator ill and applied to the vertical sweep plates 4| and 43 when the lever 38 is in its normal solid line position. Graph illustrates intermittent radiation of ultra-high frequency carrier frequency energy which is modulated at one of the modulating frequencies fl, f2 or f3 and graph l-fi illustrates that ultra-high frequency radio energy originating at the ground located transmitter and transmitted to the receiving antenna RA'l or HA2 at all times. This received energy (graph 1-5.) will not penetrate the receiving equipment unless it is modulated at one of the modulating frequencies fl, f2 or f3 and then only if the altimeter contact 57 assumes the position to select the filter 52, 53 or 54 which will pass such modulating frequency. This modulated carrier frequency is shown in enlarged form through the medium of the magnifying glass 90; A similar magnifying glass Bl has been illustrated to show on an enlarged scale one pulse of modulated radio energy emitted by the transmitting antenna TAl o'r TA2.

Ground located structures Blind route flying structure-As disclosed in our prior application Ser. No. 547,175; filed July 29, 1944, which has resulted in Patent No. 2,458,361, dated January 4, 1949, it is proposed to have each route defined by successive .fixes at each fix of which there is located suitable radio radiating means for controlling traffic indicating means on an approaching airplane. Also, as pointed out in connection with the airplane carried apparatus shown in Fig. 1 it has been proposed to radiate high frequency radio radiation of frequency Fl and to receive similar are arranged at right angles to each other and the other serving to complete a box-like structure of hollowed-out pyramid form. It is understood that a radio reflector of this shape causes the radio energy to beareflected insubstantially the same direction from which it was trans mitted thereto. It is readily seen that if such reflector 85 were mounted permanently it would reflect the same kind of radio energy which was transmitted thereto, but if this reflector were mechanically operated so as to be effective to reflect intermittently, such operation might be carried out in code fashion so that if radio energy is transmitted thereto more or less coneluding a coil 99 containing a movable core 81 acting on the end of a crank 88 which has its inner end fastened to the pivoted shaft 84 supporting the reflector 85 has been illustrated; It is readily understood that if the coil 86 is intermittently energized to characterize a code that it will'through the medium of its core 8'! intermittently operate the radio reflector 85 to positions where it is ineffective to reflect radio energy, so that the reflected energy will be coded in accordance with the intermittent energization of the coil 86. This mechanical coding of a reflector may be used to identify the fix as proposed in the prior application of Field, Wight and Saint, Ser. No. 517,814, filed January 11, 1944, or may be used to transmit conditions of traflic in advance of the fix to an airplane approaching the fix as disclosed in our prior application, Ser. No,

547,175, filed July 29, 1944.

Referring now to Fig. 4 of the drawings it will be seen that the apparatus therein disclosed includes a receiving antenna BAA and a transmitting antenna TAi. Theseantennas are preferably somewhat directional although they are not sharply focused in that energy must be re- ;ceived through or transmitted over a spread of detected energy of one or more modulating frequencies is applied to the primary winding SI of a transformer TM. The secondary winding 92 of this transformer Tr4 has of course impressed voltage thereon 0f the modulated frequency or frequencies of the radio energy received by the antenna RA4, and this current insofar as one particular modulation frequency is concerned will then pass through a particular one of the various filters 93, 84, 95 depending upon whether this modulating frequency is of frequency fl, f2 or f3.

In accordance with one form of the present invention this currentof' a particular modulating frequency is then coded by suitable coding apparatus such as disclosed in our prior application, Ser. No. 547,175, :filed July 29, 1944, and when so coded is applied to the mixer and amplifier unit I of the ground located radio transmitter including a carrier frequency generator 99. This carrier frequency generator generates a carrier frequency of frequency F2. Whether the energy emitted by the transmitter 99-400 is to be coded at a high coding rate, at a low coding rate or is to be transmitted non-coded depends upon the position of relays such as relays ALRP, ARP, CRP and TR-P the control circuits for which relays are disclosed in our prior application, Ser. No. 547,175.

It is readily seen that under normal conditions the modulated current of frequency ,f I which is flowing from the receiving apparatus to the transmitting apparatus of Fig. 4 is coded at a low rate as determined by coding disc HM and flows through a circuit including back contacts I92 and H13 of approach relays ALRP and ARP respectively. If either of these approach relays ALRP or ARP is in its energized condition the modulated current will flow to the transmitting apparatus uncoded through a circuit including either a front'contact I02 of the relay ALRP or the front contact I04 of the relay ARP, and also including front contact I05 of relay TR? and back contact I96 of relay CRP. If, on the other hand, either the relay TRP is in its deenergized condition or the relay CRP is in its energized condition current may flow through the coding disc I08 to the transmitter 99IBO to thereby code the energy of modulating frequency II at a high coding rate signifying proceed trafiic conditions.

It should be understood that under normal conditions the apparatus illustrated in Fig. 4 of the drawings continuously transmits radio energy of carrier frequency F2 but that under this normal condition this energy is neither modulated nor coded and therefore this energy cannot produce any effect on the airplane carried receiving apparatus of any airplane. If, on the other hand, this radio energy is modulated because the associated receiver 90 has received modulated energy from an airplane carried transmitter then this modulated energy may be detected by the airplane carried receiving apparatus and will produce on the fluorescent screen S (Fig. 1) thereof not only an image located on the screen in accordance with the location of the ground located apparatus under consideration with respect to the ground, but this image will also be either coded at a high or a low rate or will be left non-coded depending upon trafiic conditions in advance of the fix at which the ground located receiver and transmitter are located.

Fig. 14 modification.lf it is desired to have the ground located radio transmitter transmit carrier freouency only when radio energy is received by the associated receiver 9!] the transformer Tr (Fig. 4) may have its secondary winding 9'! connected to a full-wave rectifier IIB the output leads of which are connected across a grid bias resistance III of a push-and-pull amplifier unit as shown in Fig. 14 of the drawings. This grid bias resistance I I I acts to produce potentials to counteract the effect of the second or suppressor grid H2 in the amplifying tubes TI and T2 of a push-and-pull amplifying unit illustrated in Fig. 14 of the drawings. This push-and-pull amplifying unit is so constructed that if no current flows through the resistance III the grid bias of these tubes will be such as not to cause these tubes to function, but if direct current in excess of a predetermined minimum value flows in this resistance III the two tubes TI and T2 of the push-and-pull amplifier unit will operate to thereby apply radio energy of carrier frequency F2 to the transmittingantenna TA4. This carrier frequency F2 is modulated depending upon the modulating frequency then received by the receiver and which flows through a particular one of the filter 93, 94 or 95. This modulating current is then coded in accordance with traffic conditions in advance as determined by the approach relays ALRP and ARP and the traffic manifesting relays CRP and TRP. It should be understood that if desired, the coding in accordance with traffic conditions may be omitted and the system may be used for blind route flying and blind landing only. 7 W

Blind landing structure.-Before discussing the ground located blind landing structure illustrated in Figs. 6 to 13 inclusive it is deemed desirable to briefly refer to the airplane carried structure shown in Fig. 1 and observe how this airplane structure is used in connection with the apparatus shown in Figs. 6-13 inclusive. It will be remembered that the airplane carried structure shown in Fig. 1 is such that horizontal mechanical scanning may take place when the lever 38 is in its solid line position and that mechanical vertical scanning may take place when this lever 38 assumes its dotted position. Also, it will be remembered that a contact drum is provided to change the connections leading to the sweep plates of the cathode-ray tube K so that if the lever 38 assumes its normal position the mechanical sweep voltage derived from generator SG is applied to the horizontally acting sweep plates 42 and M and the saw-tooth voltage generated by the generator 30 is applied to the vertically acting sweep plates 4! and 43; whereas when the lever 38 assumes its dotted position the sweep voltage generated by the mechanical generator SG is fed to the vertically acting sweep plates 4i and 43 whereas the saw-tooth sweep voltage generated by the generator 40 is fed to the horizontal sweep voltage plates 42 and 44. We should now bear in mind that the apparatus shown in Fig. l and with its lever 38 assuming the dotted position functions so as to cooperate with the blind landing apparatus shown in Figs. 6-13 of the drawings. Under this condition vertical scanning is done mechanically and distances are plotted toward the right from a datum line I31 (Figs. 8-13).

Referring now to Fig. 6 of the drawings it should be understood that this is a plan view of a portion of an airport and illustrates by plan view a landing strip I20 which has, in the particular form illustrated, six radio radiators I2I, I22, I23, I24, I25 and I25 such as disclosed in Fig. 4 of the drawings associated therewith. It will be seen that the radio radiators i2I and I22 are lined up with the longitudinal middle of landing strip I 2d, the radio radiator I2I constitutingan entrance radiator whereas the radiator I22 constitutes an exit radiator for this landing strip 20. The letter A applied to radio radiators I23 and I25 signifies that the radio energy emitted thereby is coded by Morse code to characterize the letter A, and the N applied to the radio radiators I24 and I26 signifies that the energy emitted by these radiators is coded to charatcerize the letter N. It will be remembered that the letter A of the Morse code constitutes a dash followed by a dot whereas the letter N constitutes a dot followed by a dash and it is in accordance with these codes that these radiators I23--I25 have their energy coded. It may be pointed out that these codes A and N are displaced in timephase in a mannerso that the dot of the letter N will fall in the space between the dot and the dash'of the letter A whereas the dash of the letter N will fall in the space between two successive code characters A as a result of which if'both of'these codes A and N are received in like volume they will blend together to produce a continuous noncoded reception of radio energy.

Referring again to Fig. 6 the screen S shown therein is the screen S of the cathode-ray tube K.shown in Fig. 1.01 the drawings. On this cathode-ray screen S are shown and preferably em ployed two horizontal lines I3! and I32. Remembering that mechanical scanning is done vertically during blind landing it should be understood that the line I3I represents a line of sight from the airplane toward the ground at an angle of say 3 with respect to the level ground. This is on the assumption that the associated scanning antenna is stabilized in a manner as clearly described in our prior application, Sen-No. 548,660, filed August 9, 1944. The electron impinging dot I34 shown on line I33 signifies the spot on the fluorescent screen S where the radio energyreceived from the two ground located radio radiators I23 and IZt strike the screen during scannin operation of the electron beam (Fig. 1). been illustrated perfectly round and non-coded tosignify that the distances from the airplane scanning antenna to the two radio radiators I23 and I2! are exactly the same so that these two ,dots which would be present if the distances were unlike fall right on top of each other and blend out the codes so as to produce a single non-coded image as though there were only a single radio radiator, even though the spot is due to the two radio radiators I23 and IE4. It will of course be remembered that distance plotting, meaning the time consumed'in a radio impulse travelling from the airplane transmitter to the ground located receiver plus the time required for the radio energy generated at the ground location to reach the airplane carried receiver, is plotted in a horizontal direction on the cathode-ray screen S. The starting point of the electron beam sweep has been indicated by the vertical datum'line I31 on the screen S, so that the distance from this vertical line I 31 to the image I34 signifies the distance from the airplane to the ground located radio radiators I23 and I24. Had the two distances from the airplane to the radio radiators I23 and I2 5 been different the image I34 would have been divided into two different dots both located on the line I3! with one of these dots flashed to the letter A and the other one flashed to signify the letter N, and the image letter Which in the assumed case is nearest to the vertical line I37 will signify the shortest distance and therefore it will signify that the airplane is flying on that side of the centerline of the landing strip I20 where glide path l29, both shown. by exaggerated angles have also been illustrated in Fig. 7 of the draw- This dot or image I34 has.

. iz lugs and that'theseglide'paths intersect at the point I30. 1

j Operation Blind route flying operation- Although no airplane course consisting of successive ground losumed that-these ground located apparatuses one at each fix along a route will all be identical to that illustrated in Fig. 4 and that theantennas such as antennas RA4 and TM! in-Fig. 4 both located at the same fix will be so juxtaposed as to point rearwardly and upwardly .with respect to the direction ortr'avel over the route as conventionally shown iniour prior application, Ser. No. 547,175. a For convenience radio radiators IZIand I22 illustrated in Fig. 6. of the drawings may .be assumed .to' represent two fixes of a ground route. These radiators I2I. and I22-constitute apparatusessuch as illustrated in Fig.4 except that'the energy'trans mitted thereby is not coded. The radiators I23-I26 are of like construction except that their energies are cod- .edto characterize the letters A or N as the case maybe} Referring more particularly toFigs. 1 and 4 of the drawings let us assume that an airplane equipped with-apparatusconventionally as shown .in Fig. 1 of the drawings flies over an air route and cooperates with successive ground located fix apparatuses such as shown in Fig. 4 of the drawings. As conventionally shown, thetransmittingantenna 'TAi (Fig. 1) is now emitting a-carrierfrequency impulse consisting of a carrier frequency Fl modulated to a carrier .fre-

dio frequency-cycleif impulses leaves thistransmitting antenna TAI Also these pulses are preferably spacedsofar apart in time-that the preceding pulse which left the transmitting antennaTAI or TA? will have had'time to be 7 transmitted to the most remote ground located radio fix within radiating range and back again to the airplane receiving antenna RAI before a second radio impulse is transmitted from the airplane. In practice thistime in radio'distance may of course vary in accordance'with-the wishes of the practitioner of the invention and may-for example be assumed to be such a time as will .allow theeradio impulse to be transmitted to and .froma ground located fix located miles from the: airplane under consideration. It is thus seen that the apparatus disclosed in Fig. 1 is pro- "posed to transmit radio impulsesand receive in response thereto newly generatedradio impulses of a different carrier frequency, and that these impulses. are to .betransmitted for such duration and spaced such time apart that there is never .more than one impulse existing in space between the airplane and the most distant ground located apparatusinsofar as the identification of thatgparticular apparatus and fix are con,-

.-cerned.

Referring .now for a moment to the cathoderay tube .K (Fig. 1) it will be understood that the electron beam illustrated by dot-and-dash line 50 will normally impinge near. the middle bottom part of the screen as indicated by the point I50. Referring now to Fig. A of the drawings it will be observed that the wave form of the scanning voltage generated by scanning generator SGand illustrated by the graph represents a voltage which suddenly rises to a maximum then gradually falls to zero and then gradually falls to a minus value corresponding to said maximum. Since this voltage is applied to the horizontal sweep plates 42 and M of the cathode-ray tube K this scanning voltage ll! will cause the electron beam 5|] to sweep back and forth horizontally across the screen S at the very extreme lower part of the screen. This sweeping electron beam 50 will, however, not

produce an'indication on the screen because it is of such minute intensity as not to be visible, this lack of intensity being due to the fact that the grid 58 of the cathode-ray tube K is not now activated.

Referring now to the saw-tooth graph 14 shown in Fig. 5 of the drawings it will be observed that the voltage of this saw-tooth graph gradually rises from zero to a maximum and then very suddenly falls from that maximum back to zero. trated by the graph 14, and generated by the saw-tooth generator Ml, is applied to the vertical sweep plates M and 43 of the cathoderay tube K. From this consideration it is readily seen that the electron beam 58 will be lifted during the gradual climb of the saw-tooth curve 14 until it reaches the top or even beyond the top of the screen S and then will be suddenly dropped to the bottom of the screen. This dropping of the electron beam is extremely fast and the grid of the cathode-ray tube is intended to be non-activated at this time. Since the frequency of the saw-tooth curve 14 shown in Fig. 5 is many times that of the frequency of the sweep voltage graph 10 shown in Fig. 5A A it is readily seen that the electron beam 50 within the cathode-ray tube K will produce many, possibly 100 or more, very steep sawteeth on the kinescope screen, the vertical sweep of these saw-teeth on the kinescope screen S being created by the saw-tooth voltage illustrated by graph 14 and generated by saw-tooth generator 48 whereas the horizontal motion to create these saw-teeth on the cathode-ray tube screen S in succession are due to the sweep voltage conventionally illustrated by the graph lll of Fig. 5A of the drawings.

It is thus seen that the entire face of the screen S will be scanned during each cycle of the scanning voltage 'll'l (Fig. 5A) generated by the generator SG. In practice it proposed to have the scanning frequency generated by this scanning frequency generator SG high enough so that the retention of the human eye will blend successive images into a non-flickering image and this frequency in practice has been found to be required to be at least 16 cycles per second and may be as high as 36 cycles per second. Since the number of vertical sweeps of the electron beam 50 to be displayed on the fluorescent screen S should be at least 100 the scanning frequency generated by the scanning generator SG, then the saw-tooth frequency would obviously be at least one hundred times as high as the scanning frequency of scanning generator SG.

This saw-tooth voltage illusthe airplane.

the time the electron beam 50 in the cathoderay tube K starts its climb from the bottom part toward the upper part of the screen S for a particular saw-tooth scan on the cathode-ray screen S. From this it is readily seen that if the impulse emitted by antenna TAl strikes a nearby ground located fix apparatus that the re-radiated beam detected by the receiving antenna RAl will activate the grid 48 of the cathode-ray tube K earlier than would be the case if the ground located fix apparatus were located at a more distant point. In other words, the one or more ground located radiators will be plotted at distances above the lower edge of the screen S in accordance with the distances that these ground located apparatuses are from In other words, a ground located radio radiator will produce an image on the screen a distance above the lower part of the screen in accordance with the distance this ra-' dio radiator is from the airplane. Also, this image will be displayed in a horizontal direction on the screen depending on the particular scanning position then assumed by the rotating scanning antennas TA and RA. From this consideration it is readily seen that even though only a single impulse of radiant energy is emitted by the airplane carried radio transmitter and antenna that two impulses may be received from such single transmitted radio impulse. This is true by reason of the fact that the transmitted impulse may strike a plurality of ground located radio apparatuses and since the ground located radio apparatus nearest the airplane will cause its re-radiated impulse to reach the airplane first this first ground located radio radiator will have its image located at a lower point on the screen than will the image of the more distant ground located radio radiator. From this consideration it is readily seen that one or more ground located radiator images may be depicted on the same vertical line on the kinescope screen. For like reasons, a plurality of impulses may appear on the same horizontal line of the screen S. In other words, a large number of radio radiator images may be simultaneously displayed on the kinescope screen S.

In the foregoing discussion nothing has been said about the manner in which undesired radio impulses which may impinge upon the receiving antenna RAl or RAZ are prevented from afiecting the grid 48 of the cathode-ray tube K and in in the carrier frequency F2 under the condi -tion of altimeter contacts 59 and assuming their solid line position. Let us first assume that *the niechanicalscanning apparatus including the scanning motor M, transmitting antennas T-Al and TA2 and receiving antennas RAI and RA2 assume the straight-ahead position as, conventionally shown in Fig. 1 of the drawings. Under this condition there is no potential on either of the horizontal sweep plates 42 and 44 and the frequency F2 will after having beenfimp ified and detected be capable of causing eurrent fiow of modulati frequency fl through th filter 52. altimeter contact 51, wire 58 to the grid 48 of the cathode-ray tube K.

As shown in Fig; 5 a time t will have elapsed between the time the radio impulse I52 (Figs. 1 and 5) left the transmitting antenna TAI or TA2 until the received modulation I53 (Figs. 1 and 5) of modulating frequency fl reached the receiving antenna RAI or RA2. It may be assumed that during this time t the electron beams 58 in the cathode-raytube K moved from the location I50 to the location I54 (Fig. 1). From this consideration it is seen that by plotting twice the distance from the airplane to the ground located radio receiver vertically on the screen S the image electron beam 50 will assume the position I50.

on the screen S. Let us also assume that the scanning frequency current generated by sawtooth generator 48 is rapidly falling at this time, at which time an impulse of carrier frequency energy of frequency FI is generated by generator 55 and this energy impulse of frequency Fl flows into the mixer and amplifier 20, where this carrier frequency is modulated by a frequency fI 'as determined by'the tuned unit 6| which is then connected to the mixer and amplifier 20'by contact 59, from whence this modulated impulse of radio frequency Fl ,modulated at modulating frequency fl is applied to the transmitting antenna TA'l. As conventionally illustrated by the graph I52 (Figs. 1 and 5) this radio impulse will be directed through a comparatively narrow beam in 'a direction ahead of the airplane. Let us assume that this radio impulse strikes the receiving antenna RA l (Fig. 4) and is detected thereby and and may then fiow freely through the filter 93' because this filter is tunedto allow free flow of frequency fI whereas it will greatly restrict the flow of all other carrier frequencies. This current may then fiow through back contacts I02 and I03 of approach relays ALRP and ARP,

through the coding wheel IIJI, which codes the received energy at a low coding rate signifying normal trafiic conditions, from whence this current of modulating frequency fl and coded at a low coding rate will be applied to the input side of the mixer and amplifier Illll'of a radio transmitter including a carrier frequency'generator 99 generating carrier current of frequency F2. The current of modulating frequency fl will then be mixed with the carrier frequency energy'of frequency F2 so as to cause the antenna Th4 which normally transmits energy of carrier frequency F2 to be modulated during a period of time corresponding to the duration of the impulse received by the receiving antenna RA4. This modulated impulse portion of the received radio. energy of carrier frequency F2 has been shown enlarged in the magnifyingglass 88 in 50f the drawings and will eventually reach the receiving an.- tenna RAI or RA2 on the airplane, from whence this modulated portion of the. received;carrier 'of such ground located radio apparatus will be located on the screen substantially in accordance with its location in the field in advance of the airplane. That the nearer the fix is to the airplane the nearer'to the bottom on this screen will the image of this fix appear and'the farther that the fix is away from the airplane the higher will its image appear on the-screen S.

For reasons heretofore given with-reference to Fig. 4 of the drawings and particularly with ref erence to the codingwheels llll' and I08 shown therein, each of these images of groundlocated fixeswill be flashed or coded to signify traffic conditions for that altitude in advance of such fix,

.so thatthe pilot of the airplane by interpreting -these code fiashes will be informed as to traffic conditions in advance in the'particular altitude in Which h is flying.

Let us now assumethat the airplane under consideration equipped with the apparatus illustrated in Fig. 1 of the drawings has reached the airport at which it is to'make a landing. Also, that the pilot lines his airplane up with the two radiators IZI and I22 illustrated in Fig. 6 of the drawings and files low enough soas to intercept .the 3 landing glide path I28 (Fig. 7) within landing distance of the landing strip I20. The pilot will now operate his lever 38 (Fig. 1) to the dotted position to thereby cause the scanning shaft II to be disposed horizontallyand to cause drawings. 1

tention to these two images.

the connections .to the defiecting plates 4I-44 to be shifted through the medium of the contact drum 39 directly associated with the lever 38. .Vertical'mechanical scanning will now take place. Let us now consider the pilot landing his airplane with this lever 38 in its dotted position and by making reference to. Figs. 6-13 of the Blind landing operation.-As soon as the lever 38 has been operated from its solid line to its dotted position, the pilot having first properly lined up his airplane with the landing strip I28 and the radiators I2I and I22 he will find images displayed on this cathode-ray screen S of the radiators I2I and I22 but he will pay little at- He will also see displayed an image I34 (Fig. 6) due to radiators I23 and I24 and an image I due to radiators I25 and I26. If these images I34 and I35 are perfectly still and non-coded the pilot is advised thereby that he is still lined up with the landing strip I28. He will observe the spot I34 approaching' the line I3! and as soon as it reaches itsline 'I3l the pilot is aware of the fact that he is now on the 3 landing glidepath I28. He will then attempt to keep his spotl34 on this line I3! and .will also maneuver his airplane sidewise when a necessary so 'as'tokeep the spot I34 non-coded.

' airplane is assuming at that time.

l is the highest modulating frequency that should 7 be used.

The foregoing constants are merely exemplary and are not necessarily resorted to in practicing the invention. They have merely been mentioned to show how suitable constantsmay be arrived at, and it should be understood that constants of any other magnitude may be used; if desired.

Artificial horizon indicator 'As an adjunct to the blind route flying and blind landing structure already described it may I be desirable to indicate on the same cathoderay screen a line defining an artificial horizon.

. For obvious reasons this artificial horizon indication may be either used with the blind flying and blind landing apparatus already described or may be applied to a separate cathode-ray tube, and

. for obvious reasons the blind flying and landing system already described may be used without the artificial horizon indicating features pres- .ently to be described. One of the advantages of I employing the artificial horizonfeature of the present invention with the blind route flyin and blind landing apparatus is that the several 'indications will then appear on the same cathoderay screen which is believed a decided advantage in that the pilots eyes may be readily shifted ;from a blind flying indication to an artificial horizon indication and Vice versa.

Artificial horizon indicator-structure.---Before describing the artificial horizon indicating structure illustrated in Fig. of the drawings it may be desirable to refer to Figs. 16 to 23 inclusive to observe how the artificial horizon is to b indisplay the artificial horizon indication in the proper position, say near the top on the screen S under both conditions. In Figs. 16 to 19 inclusive high speed scanning is done vertically and for this reason the artificial horizon indication is superimposed on this vertical scanning whereas in the diagrams illustrated'in Figs. to 23 inclusive the high speed scanning isdone horizontally and for this reason the artificial horizon indication is superimposed upon the horizontal scanning.

Referring again to Figs. 16 to 19 inclusive it will be observed by looking at the scanning lines thereon especially insofar as Figs. 18 and 19 are concerned that suitable jogs are superimposed upon the swinging electron beam so that this beam is 'modified in accordance with banking. That is, jogs in the scanning are made in accordance with the particular banked position the Referring now to Fig. 17, firing of the electron gun of the cathode-ray tube occurs later or earlier, that is, appears raised and lowered on the screen in accordance with the nosing of the airplane at that time as indicated by the arrow I18. In other Words, the average height of the numerous dots illustrated in Figs. 16 to 19 (see arrow I18) are placed at a height on the cathode-ray screen S in' accordance with the extent of-nosing of the airplane either above or below level flying whereas the extent of slant. that these dots make on the cathode-ray screen depends on the extent of the banking of the airplane at that time. In Fig. 18 the'heavydots are slanted in a clockwise direction which indicates that the airplane is banked in a counter-clockwise direction; whereas in Fig. 19 thejheavy dots are slanted in a counter-clockwise direction which indicates that theairplaneis banked in a clockwise direction.

Referring now to Figs. 20-23 it will be observed that fast scanning takes place in a horizontal direction on the screen and it is of course understood that the heavy slanting lines shown in Figs. 22 and 23 indicate the artificial horizon under abnormal banked conditions. In'both Figs. 22 and 23 the; average height of the artificial horizon is indicated by the arrow 9- and this is dependent upon the extent of nosing of the plane either above or below level flying. In both Figs.

' 22 and 23 thisarrow is located in its normal position indicating no nosing either above or below the horizontal flying plane. It is readily understood that in the second arrangement illustrated (fast horizontal scanning) shown in Figs. 22 and 23 that the slanting artificial horizon is not placed upon the screen by placing jogs in the regular movement of the electron beam but is accomplished by firing the cathoderay tube throughout an entire high speed sweep and to fire the particular high speed sweep across the electron screen which conforms to the extent of nosing of the airplane at that time. This wouldof course result in a horizontal line across the cathode-ray screen see Figs. 20 and 21) were it not for additional apparatus to be described hereinafter to make this line slant (see Figs. 22 and 23). In order to at timesjproducea slanting line on the cathode-ray screen not only'is a particular electron beam sweep fired but it is also swung across the! fluorescent screen in a diagonal direction. In other words, in the form of invention (fast horizontal sweeping) the indications of which are illustrated in Figs. 20-23 the electron beam is swept repeatedly horizontally across the fluorescent screen at successive higher altitudes on the screen until it" reaches a height on the screen corresponding to the extent of nosing of the airplane and this particular electron sweep is then swept diagonally or slanting across the screen in accordance with the extent of banking of the airplane, the cathode-ray gun being fired at the same time.

By reviewing Figs. 16-23 it will now be readily understoodthat the extent of nosing of the airplane is indicated on the fluorescent screen by firing the electron gun at the proper point as determined by'one of the sweep saw-tooth voltages and to modify the efiect of the sweep plates of the cathode-ray tube as for instance by electromagnetic means, such as the electromagnets I15 and I16 indicated in Fig. 15 of the drawings, 'so' as to produce sweeping results in the electron beam contrary to that due to the voltage applied to the sweep plates 4! and 43.

Referring now to Fig. 15 of the drawings it should be understood that the contact drum I10 corresponds to the contact drum 39 shown in Fig. 1 of the drawings and performs exactly the same function that is performed-by drum 39 except for the fact that two additional contact suohza: gyroscope-has. been indicated by a.-gyr.o

fiy-wheer ltfl pivotally supportedfim a .box-like: framed 8-1:, which frame isrgravitationally;biased; by" a weightW-Z andby. .pivotsl (one: .only: beingshowntylfiZand is -supportedi in error 1| 53; whichv fork l'm is inturn-pivotally supported inabear-i. ing bloole l-84 fixed to the-.airplane asi by; a stub, shaft 185; This gyro I80. is spun at. a..very high speed by a suitable electric motor. or; pneumatic turbinet It is readily. understood; that if: thelairplane is banked fromitsnormaipositionthesgyro i tlhwill remain in it normal; position; and. there: fore will cause rotationof the stub shaftlfiliiin: its-fixedbearing 1:84, tothereby causeupand down movement of: the-endwofcthe bank gyroscope armdw with respect to the body .ofthe: airplane. Likewise, upward nosing ofthe. airplane willcause. thenosinggyroscope arm lette move down.- war-dly with respect to the airplane whereas,

downward nosing of the airplane.-.will cause upe ward -movernent of such-nosing gyroscope arm 1-81 This-nosing arm-I81" is provided witha contact 188 which wipes over" the. resistance leg [M -mi a potentiometer lde the other. resistance arm=-l88 -:being provided'with: a manually opera ablecontaot Isomefunctions of which will: be described- -hereinaftert- It should beinotedi that this potentiometer .189 is supported. Ibvfork 183; through the medium of brace arms i111;

The-bank gyroscope-arm I86, onthe other hand, through-themediumof the push-and-pultrod E93 QQ'GFfitGSi't-NVG SiHgIG trees I94 and: 'ldd which. are pivoted: fixedly to the airplane. asthrough. the medium-off pivotsla-t and 191; The ends-of these singletrees 1'94 and- I are pivoted to; and op.- erate-movable contacts sea and I53 insulated from single trees We and 1:95 and engage-oppo-. site sides: of a-potentiometer resistance 2%; From this construction -itis readi-ly seen that: it the single trees llld and 1%: move: inone direction tron their normal position,- ands providing. that direct current flowsin the potentiometer. resist-.. anew 2W; -volt'age of one polarity :willzbe detected by-these-contacts i98 and tile-whereas if the single trees-are moved in an opposite direction front normal the polartiy detected by. these contacted-Wand lfiswill be reversed. In practice,.a1.-. ternating current of saws-tooth configuration will beapplied to the ==-potentiometeri resistance. 2 am; sotthat it is: the-relativepolarity that i =reversed; Irr-additi'onto theapparatus already. described and illustratedin Fig. 15 'ofithedrawings there l -1 provided amplifying. tubesTlAand 'IZA. Although theJtubeTZAperIorms amplifying func tions, it is primarilyprovided touobtain currents. orpotentials whichvaryinaccorclancewithivarying voltages applied; from two. difierent-sources so--as ..to produce .a voltage ;or. currentiwhich-zis a compositetof .theetwov ineput sources. Each of: thesentubee. 'TQIAl. endz TIA; is; =.provided'; with. e.

. determines to what. extentcurrentvariations shall exist in the plate circuit-s The swcep gen orator. SG illustrated: in Fig l'fi i is t-he sama as that-illustrated: in. Fig. 1 .otthe drawingsr thatisathe -.sweep i voltage: varies: substantially: equal;

' amounts oneachsidaof-zero voltages Similariyt.

high speed sweeps sawetootitgeneraton i the same as the saw-tooth generator ditvshowmim Fig. 1 of. .the..drasving nexce tathat. this; sweep voltage .swings-.,substantially. to. equali: extents ahoveand below. zero voltagewhereas in thel ig 1'v construction. this: voltage was. intended: to varw onlvin a positive direction; Theswinging-of the: high speed sweep. voltage .both: above and below the. zero. voltage bases is:.due to the;trans/former; 'lirt'aithat.hasbeensadded in-Eig. 1'5;

Imadditionwto .theapparatusalready mentioned there are alsoishowndn Big. lfi otthe drawingstwo saturation transformers .2 a fisandimlioinvhichz the'secondary ewindingizn S a-of: the transformer 201 P1 is .connectedsthrough:rectifier RRJ to thelgr-id oftthetcathodeerayi .tube Kil when the contact; drum l'tfi assumes its normal route-fiyings posia t-ion, namely; whenithe lever sfiz'shown in Figs-r t and; 15. of the drawings essumestits solida line positiom. Theisecondaryiwinding.2OB of the saturation. transformen. Zilihisa on the-other hand"; connected i to. the grids. of: the: electron: gun of: thecathode-ray .tube.Ksi:when the apparatueassumes. itshlinddanding position; namely; when=the-leven :v ailgassumes-its.dottedmosition;.

The-primary winding. 2-! I: of transformerflkl isnormallyi connected: in thefiplate circuit includ--. ing 5 the l plate. 293; and including-.- the cathode- 211i! 0: the. .amplifyinautubetfr'lA; thistplatei circuit also. including-the ..plete -battery PBi Whereas under blind landing conditions with the-lever-Sil assuming its. dottedgpositionithe primary :Winding 2H1 ofethe saturation(transformer zilii isincludedl this; same- .plate. circuits It should be noted= wthat; the-grid. circuitincludingthe: grid 264 2 net.

cathode. 12 3230f: the amplifying tube TIA-derives: its. potential; from. the: composite potentiometee I 892. Furthermore,- it should. be observed that this potentiometer: iilQi is at all: times connected across. .and receives .energ-v. in accordance with the; voltage. applied. across the vertical sweep: platesndr. and: 4.1. but. that. this voltageduringnormal' conditions is. derived: from= the high speed scanning SELWrtOOth generatoniwhereas unden abnormal andiblind. landing conditions thevolt agetapplied. across:.the sweep plates. Ji l: end isderived; from: the; low.- .speedv scanning generator-.SG:

Referring now to the sweep electromagnets I15 and: lJzB 'it willbeobservedithat theseelectromagnets derive their energy from the secondary windingnftransformer Trfiito the-primary windingi; ofiwhich. is. includediinp series in the platecircuitmf:theamplifying.tubeTZARand =including the-plates. sourcerPBiir Thetcontrol grid" 23d ofthis: tube .TZAiswontrolled? in accordance with voltage picked oiT of potentiometer: resistance kflifl iwhich voltage isattimes of one polarity andE'at-L other. timesof the-opposite polarity depending--.- uponwhich. direction from normal the-thanked gyroscope arm I86--'is-opera-ted-,- and also-depending:up0n-=the p01arity of the voltage atxtha-t: time applied: to this: potentiometer resistance zulle b o one of the scanning volta e enerators S6201 40; The g idZiW-of membe- Artificial horizon. indicator-Route flying 020-.

Let us first consider the apparatus exactly as r r 24 duce a similar result but in an opposite direction.

Let us now assume that nosing oi the airplane downwardly, as; just 'considered has been discontinued and that thecontact 188 of the potentiometer I89 again assumes its normal position as shown in Fig. 15. Let us further assume that the pilot banks his airplane toward the left; as a result of which the bank gyroscope arm I86 7 moves downwardly. This downward movement shown in Fig. of the drawings under which condition the potentiometer I89 is fed by energy derived from the saw-tooth generator 49 whereas the potentiometer 290 derives its energy from thescanning generator SG. As shown the airplane is flying perfectly level so that the contacts I98 and I99 have zero potential applied across the same. From this it is readily seen that no energy is applied to the grid circuit of the amplifying tube T2A including grid 299, so that the electromagnets I75 and I76 are wholly deenergized in spite of the fact that grid 295 renders the tube T2A intermittently in condition to be'operable. Although the airplane is nosing straight ahead in a level course the potentiometer I89 will supply saw-tooth energy to the grid circuit or the amplifying tube TIA this is due to the fact that the manually operable contact I99 assumes a. higher position on resistance unit 'I89 'than does the gyroscope operated contact I88 on the resistance unitv I89 of the potentiometer I89. High speed sweep saw-tooth voltage is therefore appliedto the grid 294 of the amplifying tube TIA, as a result of which high speed saw-tooth voltage is applied to the primary winding 2 of the saturation transformer 297. This saturation transformer is of a construction, well known in the art, whereby transforming action takes place when a predetermined amplitude point in the magnetizing current is reached, as a result of which a very short impulse of potential is applied to the grid 48 of the electron gun of the cathode-ray tube KI at the proper point during the electron beam sweep, and this voltage-will cause the electron beam to become active each time that the elec-.

tron beam has swept to the altitude on the fluorescent screen as indicated by the arrow I78 in Fig. 16 of the drawings. It isthus seen that these various dots on the fluorescent screen will result in a horizontal line appearing on this screen at the normal height thereon as illustrated in Fig. 16 of the drawings. This normal height may be varied manually by adjusting the manually operable contact I90 of the potentiometer I89.

. Let us now observe what will happen if the airplane noses downwardly to cause the contact I88 to be moved upwardly on the resistance unit I89 of the potentiometer I89. 'This upward movement of the contact I98 will obviously decrease the magnitude of the saw-tooth voltage applied to the grid 204 of the tube TIA. Decreased voltage will cause saturation of the saturation transformer 297 to take place later in the saw-tooth cycle as a result of which firing of the electron gun will take place later and the entire row of dots on the fluorescent screen of cathode-ray tube KI will be positioned higher than-they were in Fig. 16 of the drawings, namely, they will be located. as shown in. Fig. 1'? of the draw ngs.

Obviously upward nosing will pro-' of arm I86 will cause the contact I98 to, move downwardly 0n the resistance unit 260 of the potentiometer 290 whereas the contact I99 moves upwardly on this same resistance unit. This will result in the application of scanning voltage from scanning generator SG of a'magnitude depending on the extent of banking of the airplane and of a polarity depending on the direction of such banking. This scanning voltage is applied to the control grid 2% of the amplifier tube TZA but will be inefiective to producerany plate current until the grid 205 of this tube TZA has been rendered eiiective by voltage derived 'from the secondary winding 289 of the saturation transformer 297.

As mentioned in connection with level flying and nosing by reference to Figs. 16 and 1'7 it will be seen thatlthe time of firingof the electron gun and therefore the time of functioning of the amplifier tube TZA takes place in accordance with the extent of nosing of the airplane as conventionally indicated by the arrow I78 in Figs. 1619 of the drawings. In other words, the tube T2A functions when the vertical sweep voltage has reached the. point as indicated by the arrow 178 of Fig. 18 of the drawings. Furthermore, the extent of maximum change of current flow in the plate circuit of tube T2A depend upon the particular part in the slow scanning sweep voltage cycle that is then existent. In other words, the swing of the plate current will be greatest at the'beginning and end of the slow sweep cycle derived from scanning generator SG and will be zero at the middle of the long wave of'this slow sweep cycle.

A maximum pulse of current flows inthe eiectro-magnets' I and I76 near the beginning of each slow sweep cycle, this will gradually reduce to zero by the time the middle of the saw-tooth is reached and will gradually get larger in the opposite polarity direction as the end of the sawtooth voltage curve is reached. In other words, instead of having the vertical sweep of the electron beam follow a typical saw-tooth sweep, the inclined line of which are illustrated by the lines 2 I 5 in Fig. 18 of the drawings, this electron beam will be suddenly jogged up or down as indicated by the jogs 2I6 or 2H, respectively, in Fig. 18 of the drawing; In other words, the electron beam will be located at points such as points 2I8, for instance, when firing of the electron gun takes place instead of being located in line with the arrow I78. Putting this in diiierent language the amplifier tube TIA and its associated apparatus determines when firing of the electron gun shall take place due to manual adjustment of the contact I98 or due to nosing of the'airplane "as determined from the position assumed by contact I88, whereas modified forces produced by electromagnets I75 and I76, and modifiying theefiect produced by the sweep plates 4| and 43, determine where the electron beam shall be directed at the time this electron beam is being fired;

Referring now to Fig. 18 it will be seen that the resultant dots placed in the upper'part of the fluorescent screen S will result in a. slanting line aQflJSSrllihegfhQfiQf the screen the slant. of which is dependent upon the extent of banking of the airplane whereas the1averageheight of thisrline above; or. belowHnor-mal (see arrow I18) is dependent: onthe, ,extent of nosing below or above leveltflying, respectively.

If the pilot now banks his airplane toward the right he will cause upwardmovement of the bank gyroscope arm I86 with respect to the airplane, thereby causing upward movement of the contact l'fih'anddownward movement of the contact I99 .sothat-the saw-tooth voltage applied to the grid 204 of=1 the Tube T2A will be of oppositerelative polarityfrom that when he banked toward the left. This will obviously cause the line produced -on -jthec-fluorescent screento be slantedv in the opposite direction as indicated in Fi 19 of the drawings.

It should be understood that this production of animage ofan artificial horizon on the fluorescent screen will not interfere with PTOPEIliQdication of the route during route flying operation asdescribed in connection with Fig. 1 of the drawings because the artificial horizon will only appearin the upper part of this screen whereas route indicating images will only appear in the lower part of the fluorescent screen.

Artificial horizon indicator-Blind landing opera-tion;-Let us now assume that the lever 38 shown in Figs. 1 and 15 of the drawings is moved to'iitsdotted position. This will not only cause the-axis of the mechanical scanning shaft H (Figs 1) tube moved to a horizontal position but will also-causethe drum I10 (Fig. 15) to be perated to the reverse position. This reversing of the drum I causes the low speed scanning generator SG to be connected to the potentiometer I 89-whereas the high speed saw-tooth genera-tor 40 through transformer 'I'r5 has its output circuit connected to the potentiometer 289. And furthermore, this operation causes the low speed scanning-generator SG to supply energy to the vertical sweep plates M and 43 of the cathoderay-tube KI and causesthe high speed saw-tooth voltage generator 40 to be connected to horizontalsweep plates 42 and 44. Furthermore, this operation of the contact drum I10 to its abnormal position causes the saturation transformer 2% to be'substituted for the saturation transformer 281. This "saturation transformer 2%, the primary winding 2190f which is now included in series in the plate-circuit for tube TIA, is energized by current related to the low speed sweep voltage derived from-generator SG' because the grid circuitof tube TIA derives its potential from potentiometer I89 and this potentiometer we is now connected across this low speed scanning generator SG.

'If we now assume thatthe airplane is flying level and that high speed scanning in a horizontal-direction across the fluorescent screen ,is taking place, the lever 38 assuming its dotted position because blind landing operation is being contemplated, we-will observe from Fig. 20 that during-- one complete horizontal sweep of the electron beam-across the fluorescent screen is rendered visiblebecause the electron gun of the cathode-ray tube is being fired throughout this entire sweep. The particular high speed sweep of'the electron beam across the fluorescent screen thatisrenderedvisible is determined'by the time of induction of current in the secondary winding 2 .99. tof the; saturation transformer 201 and this isdependenton theamplitude of the voltage then appliedi between, the contacts I 88- and I an of the potentiometer I89. Since this potentiometer I89 is now connected-across, the low speed scanning generator SG only one firing-of the electrongun willtake. place during each complete scanning of the fluorescent screen. The time of firing is determined by the amplitude of this low speed sweep voltage whichis also in part dependent on the construction of the saturation transformer 2%. The apparatus is so constructed that for the sameadjustment of the manually operable contact It'dand the automatically. operable contact its oil-potentiometer. I89 which causedthe Fig. lit-indication will cause firing to take place at a height on the fluorescent screenv as indicated by arrow I19 in Fig. 20 of the drawings. This height. indicated by arrow I19 in Rig. 20 is the same as thatjindicatedby the arrow ITBWlnEig. l5-of1the drawings. 'In other. words, with the layer 3 8: assuming its dotted position the potentiometer I89, thefsaturation transformer 206, and the amplifying. tube .TI,A determine at which time innalow speedsweep of the electron beam the electrongun of the cathode-ray tube shall be fired.

Since under. the condition just assumed the contacts 198 and I99 of potentiometer 200. are located at .thesame point on the resistance unit 299 no voltage is'applied to the control grid 294 of thelamplifying tube TZAsothat no currentwill be produced inthe electromagnets I15 and I16. From this consideration it will be, un derstood that the particular sweep, horizontally across the. cathode-ray screen which occurred when firing of the electron gun took place was a perfectly horizontal. sweep,.because thesweep plates ill. and. .43 alone determined the vertical positionof the electron beam throughout its entire horizontal. sweep at this ,time, because the electromagnets, I15 and I16 which could' have modified. the actionof these sweep plates 4| and 43 'producedno suchaction because. these electromagnets. I15. and I16. were deenergized.

Let us now assume that the airplane under considerationnoses upwardly. as. a result of which the contact I88 moves downwardly on the resistance unit I89 of the potentiometer I89. This will cause increased amplitude of saw-tooth voltage tobe picked off of potentiometer I89 bycontacts I88 and I99. This increased saw-tooth voltage will cause the saturation transformer 208 to function earlier-during a low speed sawtooth voltage sweep and therefore will cause firing to take place earlier in an upward movement of the low speed scanning sweep of the electron beam, so that the horizontal line during whichfiring 'takesplace will be located lower on the screen as is indicated by the heavyline' in Fig. 21 of the drawings.

Let us now assume that the pilot banks his airplane to the left (direction of travel toward right in Fig; 15) to thereby cause the bank-gyroscope arm I 86 to-be moved downwardly with respect to theairplane. This will cause the contact I98 to move downwardly and the contact $99 to move upwardly on the resistance unit 200 of the potentiometer 200. Since this potentiometer 290 now receives itsenergy fromthe sawtooth generator and since the contacts I98 and I93 are positioned to pick ofi ofpotentiometer 2&9 such asaw-tooth voltage this saw-toothvoltage'by being applied to the controlgrid 2040f the amplifying'tube'TZA will produce energy' in the-plate circuit of this tube TZA only when this tube T2A is rendered activatable by the application of potential to itsgrid 205. Since-thispowill be modified by'the action produced by the electromagnets I15 and H6. These electromagnets derive their energy from the transformer 'IrE the primary winding of which is included in the plate circuit of the tube TZA. From this consideration it will be apparent that the artificial horizon indication on the screen S will be slanting dependent upon the amplitude of the saw-tooth voltage picked off of potentiometer 260 which in turn depends on the extent of banking of the airplane as indicated in Fig.'22 of the drawings. The average height of this slanting line of, course depends on the manual adjustment of contact I90 and the extent of nosing of the airplane. Had the airplane been banked in the opposite direction the direction of current flow in the electromagnets I15 and I16 would have been of reverse polarity and the slant of the illuminated sweep would have been in the opposite direction as indicated in Fig. 23.0f the drawings.

In the foregoing discussion relative to Figs.

20-23 it was assumed that firing of the electron gun'of the cathode-raytube Kl would extend only during one complete horizontal sweep of the electron beam. It should, however, be understood that if the current impulse supplied to the grid 48 of the electron gun lasts for several sweeps that under this condition several cycles of saw-tooth current will flow in electromagnets "Sand I16 to cause several slanting sweeps to take place across the fluorescent screen S during banking of the airplane for each complete scanning of this screen S. If desired therfiring impulses may be made long enough to cover more than one complete horizontal sweep. If desired that part of the fluorescent screen S on which the artificial horizon is indicated may produce an indication of different color. For image color determination attention is directed to page 344 of Radio Engineers Handbook above referred to.

By referring to Fig. 1 of the drawings it will be observed that receiving antennas RA have been shown separately from the transmitting antennas TA. It is readily understood that since it is not contemplated to have transmission and reception to take place at the same instant suitable counter voltages may be induced into the receiving apparatus so as to neutralize the eifect due to directly applied transmitting voltages caused by cross radiation. If desired, therefore, the receiving antennas may be dispensed with modifications comewithin thescope of the following claims. 1

What we claim as newis:

1. In a navigation system for airplanes, an airplane'carried cathode-ray tube including a screen, an electron gun for creating an electron beam and sweep structure for sweeping said electron beam in planes at right angles to' each other, a transmitting and receiving antenna sys-' tem effective to scan in one of the planes a verti-' cal area in advance of the airplane, a sweep voltage generator operated in synchronism with the scanning by said antenna system and connected to sweep saidelectron beam in the plane in which the antenna scanning is effective, a pulse generator generating pulses at a, rate much higher than the frequency of said sweep voltage generator, an altimeter switch for automatically selecting a' distinctive modulation frequency in accordance with the altitude of the airplane, a modulated'carrier frequency generator for generatingcarrier current selectively modulated in response to the modulation selected and a single pair of antennas may be used for departing from the invention so long as these by said altimeter switch, said carrier frequency generator being effective in response to the respective pulses of said pulse generator to apply carrier wave pulsesto said antenna system for transmission, a saw-tooth sweep voltage generator controlled in response to the respective pulses of said pulse generator and connected to sweep said electron beam in a plane at right angles to the plane of scanning by said antenna system, means for rendering said electron gun active in response to the reception of radio energy only when modulated at the modulation frequency selected by said altimeter switch, and ground located means effective in response to radio energy transmitted by the airplane for immediately retransmitting to the airplane radio energy of the same modulated frequency as is received. Y

2. In a navigation system for airplanes, an

airplane carried cathode-ray tube including ascreen, an electron gun'for creating an electron beam and sweep structure for sweeping saidelectron beam horizontally and vertically, a transmittingantenna and a receiving antenna both constructed to scan horizontally an area in ad vance of the airplane, a sweep voltage generator operated in synchronism with the scanning of said antennas and connected to'sweep said electron beam horizontally, a pulse generator for generating pulses at a rate substantially higher than the rate of scanning of said antennas, an altimeter switch effective to select a distinctive modulation frequency in accordance with the altitude of the airplane, a modulated carrier frequency generator for generating carrier current selectivelymodulated in accordance with the modulation frequency selected by said altimeter switch, said carrier frequency generator being'rendered active in-response to each pulse of said pulse generator to apply energy to said transmitting antenna for radiation, a saw-tooth sweep voltage generator controlled by said pulse generator and connected to sweep said electron beam vertically for each pulse of said generator, means for rendering said electron gun active in response to the' reception of radio energy by.

airplaneacarrierewavemodulatedbyithemodulaa no frequency that hasnbeenreceived;

3:1In =.a:navigation system for airplanes'of the" character: described, an airplane. carriedicathoderaytube including ascreen, an electron gun: for

an electron beam and sweep structure for swoeping said electron. beam horizontally and vertically;a transmitting and" receiving scanning antenna system. normally. active to. repeatedly scan-the area in advance of the-airplane. 'horizonta'lly, asweep: voltage, generator operated. in synchroni'sm withrotation of said antenna system andiiconnected to sweep said electron beam.

horizontally," a. pulse. generator 'for generating pulsesrata frequencysubstantially higher than the frequency of j-said. Esweep voltage :generator,

an i ai-rpiane carried "altimeter. switch. for auto-'- maticaliyv selecting. a. distinctive modulation frequency inaccordance with. the altitude of the airplane, a: modulated: carrier frequency generator for generating: carrier current 1 selectively modulatedrin.accordance with the position of said-altimeter .1 switch, said carrier frequency generator; being rendered intermittently. active in response:tdsaidpulsegenerator to applyits out-- put-ntovsaidtantenna system for transmission, a sawetooth-sweep voltage generator controlled by saidrpulselgenerator andconnectedrto sweep said electrombeam vertically once for each. pulse of saidiipulsexgenerator, means for rendering: said electronzguna active in response .to the reception ofzzradioenergy by said antenna. :system, only provided-what such'radio. energy is. modulated at the::friaquencmselected by saidraltimeter switch, andagroundi located meansnat. respective stations spacedralong anjairway effective kin response to radio energy transmitted by respective airplanes.

tosi'immediately retransmit. radio energy of the same: modulated? frequency as was. received; whereby: an indication. is displayed on said' screen as:;to:-the azimuth: of" the airplane. heading with respect to thesrespective groundastations with which the airplane. is. communicating and as :to. the; :distance; that: airplane is. from I such ground onsftnansmis'sion'to airplanes at other'altitudeson StalliOnSf,lla11T without interference by simultanee tem and connected to sweep said electron beam of saidicathbde-ray tube in one plane, a pulsegener ator effectiveto generating pulses at a frequency many.'times .that.of"the frequency of said sweep voltage generator, a carrier frequency generator rendered intermittently "active. in response to the-respective pulses of said pulse'generator; the

outputiaofasaid: carrier frequency: generator being appliedato: said antennarsystenr for the intermittent radiatiomof. carrier-waves, a saw-tooth sweep voltageugenerator:controlledby said pulse gen eratonandaconnected. to :sweep said: electron-beam anright anglesto the directionin which :the elecw trombeam: is: swept: by the. output of: said :sweep r voltagergeneratori means icr-rendering said elec-" tronwguniactire in 1 response: to the reception of radio energy: of :a particularcarrier. iirequencyby; said;antenna:systemgmundlocated:receivingand:

transmitting .meansxesponslve to radio-"energy? radiating from an airplane for; retran'smitting radio energy to: the. airplane, and switching structure of saidicathoderraytube.

5.. Inaroute" indicating :and landing system for airplanes, anairplane carried. cathode-ray tube including a :screen; an electron :gun for creating anselectron beam and sweepstructure for sweeping .saidielectron beam, horizontally and vertb cally; an airplane .:carried' Itransmitting'and re- .ceiving antenna systemzconstructed' to-scan either a -narrow rectangular horizontal area or anarrow rectangular vertical-"area as selected, 1 a sweep voltage generator operated in synchronism witns the scanning of said antenna system irrespective ofwhether or not a horizontal or: a vertical area i a.being..scanned',za pulse generator for generat ing pulses. at a ratezmanyxtimesathe frequency of sai'd' sweepivoltage', a carrier frequency. generators rendered intermittently active in responsetothe respective pulses of said pulse generator and connected to apply'carrier current: to said antenna system for radiation, a saw-toothrsweep: voltage generatorcontrolled by the respective" pulses of said pulse generator for sweepingisaid electron beam horizontally or vertically as .selected, means for rendering said electron gun active in response .to the reception of radio energy bysaid antenna system, ground located receiving and'transmitting means for retransmitting radio energy. in response to energy. received fireman airplane, T and. manually operable means for se lecting said antenna system to: scan said hon: zontal or said vertical area; said manually oper able. means. being simultaneously effective to selectzthe governing of said horizontalandverticalsweep structures by said sweep generator or said saw=toothz generator, whereby the scanning'of thexhorizontal rectangular areaby the antenna" systemican'beselected for coursefiyingyand the scanning of the" vertical rectangular area by the 1 antenna system can beselected for blind landing on a glide path;

6; In" a navigationsystem for'fiying along an" airway, the combination with a plurality of radio transmitting; andreceiving ground stations spaced'along the airway, of'a irplane carried"apparatusz. comprising, a cathode-ray tube having a screen i and: an electron gun and horizontal and vertical: sweep-structures; a first electron'gun con-trolameans-including radio transmitting-Land receiving meansefiective to govern the intensity of the. electron "beam formed by saidelectron gun in: accordancewith pulse communication with the respective ground stationsthorizontat sweeprcircuitmeans governed by said transmittingzand receiving means effective to plot on said screen" along :a horizontal coordinate substan-' tially; the: azimuth of the respective 'ground"'sta= tionstinfadvance of 'the airplane, verticalsweep circuit" means governed'by' said" transmitting and receiving: means for plotting distancesof the airplane from the respective ground stations on said screen-along a vertical coordinate; a second electron gun control means effectivewhen render edcactiveto-govern the intensity of the electron beamrformed by said electron gun in accordanoe with'another indication to be displayedon said screen, and'meansrendering said second electron gunicontrol means (active for eachvertical sweep of-csaidi vertical sweep-circuitxneans; only 'subse 

